The present invention is directed to an expansion dowel assembly for use in undercut bores in a receiving material for securing a structural component by means of an anchor bolt to the receiving material. The anchor bolt has an axially extending load application section extending from one end and an expansion cone fitted to the other end. An expansion sleeve to be placed in the undercut bore is at least partially slotted from a leading end. A guide sleeve having an outside diameter corresponding to the outside diameter of the expansion sleeve encircles the anchor bolt at its end with the load application section. The expansion cone on the anchor bolt can be pulled into the expansion sleeve for expanding it into the undercut bore.
An expansion dowel, disclosed in EP-Al-0226 524 includes an anchor bolt having an expansion cone on one end and a load engagement section in the form of an external thread at the other end. The external thread is arranged to receive a nut. Two tubular-shaped sleeves are arranged between the expansion cone and the nut with the sleeves having an outside diameter corresponding to the diameter of the bore in a receiving material into which the expansion dowel is to be anchored. The smallest inside diameter of the sleeve is slightly larger than the shank diameter of the anchor bolt.
The sleeve closer to the expansion cone called the expansion sleeve in the following description, has axially extending slots running opposite to the setting direction from an end face of the sleeve directed toward the expansion cone. The axially extending slots form individual expansion sections to be radially widened by the expansion cone.
The sleeve located rearwardly of the expansion sleeve is called a guide sleeve in the following description and serves for radial guidance of the anchor bolt into the bore.
During the expansion process, a structural component to be fastened to a surface of the receiving material can be placed against the receiving material. A through opening in the component has the same or slightly larger diameter than the bore in the receiving material.
The expansion sections of the expansion sleeve are radially widened into the undercut portion of the bore by a suitable setting tool and by the expansion cone positioned on the anchor bolt. After the expansion sections are expanded, the setting tool is removed and the guide sleeve is slid into the bore over the anchor bolt.
The trailing end face of the guide sleeve can enter into the bore to such an extent that the transverse forces generated by the component bearing against the receiving material cannot be carried by the guide sleeve. Such a guide sleeve does not assure either a reliable centering of the component on the receiving material or a reliable support of a laterally directed load generated by the component. As a result, the effectiveness of the attachment is questionable, since an alignment of equal area of the trailing end face of the guide sleeves and the surface of the component located opposite the receiving material is not assured.
If the guide sleeve does not project into the range of the component in contact with the receiving material, the component can displace itself in the load application direction if a higher lateral load occurs, until the wall of the through opening of the component bears against the anchor bolt, whereby the anchor bolt is obliged to carry the entire lateral load. In superposition or overlap of the constant axial force generated during attachment of the component to the receiving material, an additional shear force acting perpendicularly thereto can result in an overload and may lead to a fracture of the anchor bolt.